Printed circuit boards (PCB's) with electrical components are widely used in the electronics industry in a variety of products including computers, servers, televisions and telecommunication devices. In the early days of these electronic products, components, such as microprocessor central processing units (CPU's), secondary PCB's, also known as daughter cards, and other major electrical components, were all soldered directly to a primary PCB, also known as a mother board. Although this was a cost efficient mounting method as far as manufacturing was concerned, there was a major drawback. If the component (for convenience to be referred to as a daughter card hereinafter) was found faulty later or a user wanted to upgrade the daughter card, the daughter card had to be unsoldered from the motherboard and a new one resoldered in its place. As daughter cards grew more integrated and sophisticated, the number of solder connections between the motherboard and the daughter card increased, greatly complicating replacement. Moreover, the heat generated during the unsoldering and resoldering process sometimes overheated the motherboard and/or the daughter card rendering them useless or limiting their lifetime.
Because of the above-discussed deficiencies of direct solder mounting of daughter cards, CPU's, etc., low insertion force (LIF) electrical connectors comprising a socket component and a pin component were developed. The LIF socket components were designed to be directly soldered to the motherboard in lieu of soldering the daughter card thereto. LWF sockets provided a plurality of apertures on an upper surface thereof for receiving the pins of the LIF pin component which was soldered directly to the daughter card or was made integral therewith. Each of the apertures contained a spring loaded contact that frictionally gripped each pin as it was inserted. The combined frictional forces of all of the spring-loaded contacts on the pins retained the LWF pin component in the LIF socket component and provided for good electrical contact between the motherboard and the daughter card.
As component size and pin count continued to grow, however, LIF electrical connectors became problematical. The design of LIF electrical connectors required keeping individual aperture friction of the LIF socket component to a minimum to keep total LIF pin component insertion/extraction force to a practical level. However, each spring loaded contact in the LIF socket component required a certain amount of spring force to maintain reliable electrical contact with the respective pin of the LIF pin component. Therefore, as pin count grew, the total spring and frictional force also grew. At some point, the combined frictional force of all of the spring loaded contacts made insertion or extraction of the LIF pin component of the daughter card from the LIF socket component of the motherboard difficult. Sometimes, the required insertion/extraction force bent or folded slightly misaligned pins, placing the entire daughter card at risk. If the insertion/extraction force was not applied uniformly, pins were at risk of being broken. As such, often a special purpose removal tool was required for extracting LIF pin component equipped daughter cards from the LIF socket component equipped motherboard.
Today's electronic products are often designed to operate with improved components (i.e., daughter cards, CPU's, etc.) as they are developed. For example, as an improved daughter card becomes available, a user wishing to increase a PC's performance need only replace the existing daughter card with an upgraded model. Unfortunately, due to the high extraction/insertion forces, many users lack the ability and removal/insertion tools necessary to remove and install LIF pin component equipped daughter cards from LIF socket component equipped mother boards.
In response to this need to upgrade electronics products, zero insertion force (ZIF) electrical connectors were developed. ZWF electrical connectors eliminated the need for the user to apply substantial insertion/extraction forces to upgrade electronics products. Like, LIF electrical connectors, ZIF electrical connectors comprise a socket component and a pin component. Like LIF socket components, ZIF socket components are designed to be directly soldered to the circuit board. ZIF socket components also provide a plurality of apertures on an upper surface thereof for receiving the pins of the ZIF pin component which was soldered directly to the daughter card or was made integral therewith. However, unlike an LIF socket component, the apertures of a ZIF socket component do not contain spring loaded contacts, but accept each pin of the ZIF pin component without substantial frictional resistance. Each aperture of the ZIF socket component includes a rotatable cam. Insertion of the pins of the ZIF pin component into the apertures of the ZIF socket component causes rotation of the cams. This places the pins of the ZIF pin component in a mechanical shear or bind within the apertures of the ZIF socket component. The mechanical bind brings about a reliable electrical contact for each of the pins and apertures, but allows a ZWF pin component equipped daughter card to be readily removed from a ZIF socket component equipped motherboard.
Since the mechanical bind between the pins and apertures of the ZIF electrical connector components is sometimes insufficient to adequately secure the daughter card to the motherboard, other retention mechanisms are employed to accomplish this task. These retention mechanisms typically employ a heat sink that is positioned atop of the daughter card. Mechanical fasteners or lever arms of the retention mechanism that act between the heat sink and the motherboard are then used to adequately secure the daughter card to the motherboard. In this arrangement, the daughter card is in essence “sandwiched” between the heat sink and the motherboard and is held in place by the retention mechanism.
One drawback of this arrangement is that the weight of the heat sink together with the clamping forces provided by the retention mechanism tends to place solder joints, especially the solder joints between the ZIF socket component and the mother board, under compression loading. This compression loading has proved to be problematical, since this compression loading, together with thermal and power cycling, which occurs during use of the mother board/daughter card, tends to adversely affect the integrity of the solder joints between the ZIF socket component and the mother board. In other words, compression loading, power cycling and thermal cycling tends to cause fractures in the solder joints that can weaken the electrical connection between the ZIF socket component and the motherboard. These weakened electrical connections lessen the reliability of the daughter card and mother board interconnect, and the overall reliability of the electronic product employing the motherboard/daughter card, thereby rendering the electronic product useless or at least limiting its lifetime.
There is a need for improved PCB assemblies. In particular, there is a need for an improved PCB assembly that provides a reliable electrical connection between the daughter card and mother board. This electrical connection should not be readily susceptible to deterioration as a result of compression loading, power cycling and/or thermal cycling. Lastly, the PCB assembly should be relatively easy and inexpensive to manufacture.